Among the discovered carbon allotropes, diamond has long been a material of interest for research due to its unique properties. Of all known materials, it is the hardest and has the highest thermal conductivity (Spear, K. E., J. Am Ceram. Soc. 1989, 72, 171-191). Its wide band gap, high electron and hole mobility, and negative electron affinity (NEA) make it an attractive candidate for use in ultraviolet (UV) light detectors and emitters (Koizumi, S, et al., Science 2001, 292, 1899-1901), radiation particle detectors (Monroy, E. et al., Semicond. Sci. Technol, 2003, 18, R33-R51), field effect transistors (Isberg, J. et al., Science 2002, 297, 1670-1672), electron field emission sources (Okano, K., et al. J. Nature 1996, 381, 140-141), position-sensitive biochemical substrates (Yang, W. et al., Nat. Mater. 2002, 1, 253-257), and many other possible applications, including those subjected to harsh environments such as high temperatures or high-power devices for space applications.
Techniques for growing crystalline diamond have evolved from the high-temperature high-pressure (HTHP) method (Bundy, F. P. et al., Nature 1955, 176, 51-55) to plasma enhanced chemical vapor deposition (PECVD) techniques that typically operate at 120-220-Torr and 900-1500° C. followed by microwave annealing at high temperature (Meng, H. K. et al., J. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 17620-17625). Diamond microwires with 25 μm diameter and 400 μm length were synthesized in 1968 using a radiation heating unit developed from a super-high pressure xenon tube (Derjaguin, B. V. et al., J. Cryst. Growth 1968, 2, 380-384). Some top-down approaches employed include reactive ion etching to fabricate diamond nanowires 3-10 nm in length (Yang, N. J. et al., Nano Lett, 2008, 8, 3572-3576), and using porous anodic aluminum oxide as a template to form a diamond cylinder array (Masuda, H. et al., Adv. Mater 2001, 13, 247-249). Post-treatment of carbon species and PECVD techniques have been used to make diamond nanorods of low crystallinity of up to 200 nm in length (Sun, L. T. et al., Adv. Mater. 2004, 16, 1849-1853; Vlasov, I. L. et al., Adv. Mater 2007, 19, 4058-4062; Shang, N. et al., ACS Nano 2009, 3, 1032-1038). Diamond nanowires have also been the subject of various theoretical studies and structural simulations. (Barnard, A. S. et al., Nano Lett. 2003, 3, 1323-1328; Barnard, A. S. et al., Chem Phys. 2004 120, 3817-3821; Wang, C. X. et al., Mater. Sci. Eng., R 2005, 49, 157-202). Synthesis of crystalline diamond nanowires is of major interest since they offer the potential for enabling applications across many disciplines, for advancing the science of material synthesis at the nanoscale and atomic scale, and for validating the search for new forms of carbon. However, the fabrication of long, single crystalline diamond nanowires using conventional thermal CVD methods has so far proven elusive despite the potential benefits.